Hypersaline Coastal Lagoon Research Articles

Cyanotoxins in Epipelic and Epiphytic Cyanobacteria from a Hypersaline Coastal Lagoon, an Environmental Hazard in Climate Warming Times and a Potential Source of New Compounds.

Cyanobacterial biodiversity and potential toxicity in coastal lagoons have barely been studied despite these transitional water systems being very important in conservation and for the preservation of economic resources. Most of these transitional systems have been affected by eutrophication, and climate change will severely affect them by promoting cyanobacteria growth, especially in Mediterranean areas. This study aims to characterize the diversity of epipelic and epiphytic cyanobacteria species in a Mediterranean coastal lagoon and their potential for toxins production (microcystins and saxitoxins). Strains were isolated and genetically identified. Toxins were extracted and quantified by LC/MS-MS. All the taxa belong to the former Oscillatoriales. The presence of Nodosilinea and Toxifilum is reported for the first time for Spanish waters, but Pseudanabaena, Phormidium, Geitlerinema and Synechococcus also formed part of benthic mats. All the strains contained Microcystin-YR (MC-YR), but saxitoxin (STX) was present only in the extracts of Nodosilinea and Pseudanabena. MC-LY, MC-LW and [D-Asp3] MC-LR were detected in the extracts of Synechococcus and MC-LF in Toxifilum, but at concentrations that did not permit quantification. Toxins production by epipelic and epiphytic strains in coastal lagoons may represent a hazard, but also an opportunity to obtain potentially interesting compounds that should be further studied.

Organic matter accumulation drives methylotrophic methanogenesis and microbial ecology in a hypersaline coastal lagoon

AbstractHypersalinity is common in coastal wetlands throughout warm, tropical, and arid regions. Climate‐induced changes in rainfall, sea level, and anthropogenic modification to basins and coastlines are likely to further increase salinization in these ecosystems. Yet, carbon cycling in hypersaline coastal wetlands is not well understood, and poorly constrained in climate models. In the Coorong, a eutrophic, hypersaline coastal lagoon, recognized as internationally important under the Ramsar convention, organic matter rapidly accumulates in deeper areas of the lagoon, through the settling of fine detrital particles, phytoplankton and suspended sediments. During initial surveys, elevated surface water methane (CH4) concentrations were observed above these fine depositional sediments. To identify the drivers of CH4 production, organic matter and sediment characteristics were assessed in surface sediments. Genetic markers (i.e., 16rDNA and the mcrA functional gene) were used to characterize microbial communities. With multiple lines of evidence, this study identifies organic matter, methanogen abundance, and salinity as important drivers of CH4 production, which is concentrated in depositional zones. Archaea were also more abundant in depositional zones, including methylotrophic methanogens: Methanofastidiosales, Methanomasiliicoccales, Methermicoccaceae, and Methanococcoides. These methanogens were highly correlated to CH4 in porewater, suggesting an influence of methylotrophic methanogenesis. To investigate further, metabolic genes were predicted from 16S rRNA with PICRUSt2. This represents the first effort to analyze CH4 dynamics in the Coorong, underscoring the need to integrate these unique ecosystems into global climate models to enhance our understanding of greenhouse gas dynamics and emissions in a changing climate.

Tidal, density and wind-driven subtidal circulation in a hypersaline coastal lagoon

Subtidal circulation patterns were studied along an elongated hypersaline system. Month-long data were collected using three acoustic Doppler current profilers. These profilers were moored at depths of around 15 m in three locations: 10 km inland from the mouth of the lagoon, within the central region, and near the head of the lagoon. The variability of temporal and spatial subtidal circulation was explored using Empirical Orthogonal Functions analysis, which explained 93% of the variability through the first three modes. The first mode was influenced by tidal advection, resulting in a tidally-driven residual circulation for elongated channels, with inflows occurring over the shoals and outflows in the deeper channel sections. During the neap-tide cycle, inverse density gradients became relevant, coinciding with the peaks of mode 2 amplitude that accounted for 15% of the total variability. The gravitational circulation exhibited its highest intensity near the head, characterized by a vertically sheared flow with inflow occurring near the surface and outflow underneath. Predominant onshore wind stresses had a significant impact on the subtidal circulation and displayed a strong correlation with the mode 3 amplitude, explaining 11% of the total variability. Wind-driven circulation exhibited a vertically sheared profile, characterized by downwind near-surface flow and upwind flow underneath in the lagoon mouth and head, and a homogeneous downwind profile in the central part of the lagoon. It is concluded that tidal stresses governed the subtidal circulation, followed by density gradients, and wind stresses modified spatial circulation patterns induced by tides and density gradients. This research provides new observational evidence on tidal residuals in long channels and contributes to the understanding of the interactions between the main subtidal circulation drivers in hypersaline lagoons.

Ecological and environmental characteristics of a seagrass-dominated hypersaline coastal Mediterranean lagoon: a multidisciplinary approach

In the present paper, sedimentological, water physicochemical data and biological benthic assemblages are compiled to provide an integrated environmental assessment of a protected shallow Mediterranean lagoon with a long history of management interventions (Klisova Lagoon, Western Greece). Satellite remote sensing techniques were used for mapping the seagrass Cymodocea nodosa (Ucria) Asch, which presents an extensive expansion in the study area. The results showed that Klisova is a hypersaline, well-oxygenated lagoon presenting changes in temperature, salinity, pH and dissolved oxygen over the course of 1 year, but largely lacks any spatial differentiation other than an east–west gradient in salinity in spring and summer. Sediment was classified as silty sand to silt, rich in total organic carbon (TOC), total nitrogen (TN) and total phosphorus (TP). The benthic community was characterised by a high species richness and the presence of marine species, without a clear spatial pattern. The multivariate-AZTI’s marine biotic index (M-AMBI) showed that the ecological quality of the macrobenthos was good in most stations. C. nodosa covered over 70% of the lagoon area and formed meadows even in the eastern part of the lagoon where salinity during spring and summer was close to the reported upper tolerance limit of the species (> 50). The present multidisciplinary approach provides valuable baseline information on various components of the ecosystem which can be used as a basis for management bodies and future conservation plans for the lagoon.

Measuring Marine Biotoxins in a Hypersaline Coastal Lagoon.

Marine biotoxins have posed a persistent problem along various coasts for many years. Coastal lagoons are ecosystems prone to phytoplankton blooms when altered by eutrophication. The Mar Menor is the largest hypersaline coastal lagoon in Europe. Sixteen marine toxins, including lipophilic toxins, yessotoxins, and domoic acid (DA), in seawater samples from the Mar Menor coastal lagoon were measured in one year. Only DA was detected in the range of 44.9-173.8 ng L-1. Environmental stressors and mechanisms controlling the presence of DA in the lagoon are discussed. As an enrichment and clean-up method, we employed solid phase extraction to filter and acidify 75 mL of the sample, followed by pre-concentration through a C18 SPE cartridge. The analytes were recovered in aqueous solutions and directly injected into the liquid chromatography system (LC-MS), which was equipped with a C18 column. The system operated in gradient mode, and we used tandem mass spectrometry (MS/MS) with a triple quadrupole (QqQ) in the multiple reaction monitoring mode (MRM) for analysis. The absence of matrix effects was checked and the limits of detection for most toxins were low, ranging from 0.05 to 91.2 ng L-1, depending on the compound. To validate the measurements, we performed recovery studies, falling in the range of 74-122%, with an intraday precision below 14.9% RSD.

Benthic mollusc communities across space and through time in a hypersaline coastal lagoon, Mexico

The coast of the Yucatan Peninsula (Mexico) has undergone numerous changes over the last century as a result of population growth, shifts in land use, establishment of industries, and storm impacts. To understand how the mollusc fauna responded to these changes over time, paleoecological studies were conducted to compare historical and modern data, and to reveal information on past environmental conditions. We analyzed mollusc assemblages in sediment cores from Río Lagartos coastal lagoon, which span the last ∼70 years. Mollusc assemblages in the sediment cores were compared to a modern inventory of Mollusca fauna, which was compiled to assess species distributions associated with multiple environmental variables. Mollusc assemblages from the sediment cores (17,089 specimens), which represent 19 bivalve and 43 gastropod species, and modern inventory datasets possess the same ubiquitous species and the same feeding guilds, i.e., groups that exploit the same food resources. Nearly twice as many species were identified in the sediment cores as in the modern inventory. This finding probably reflects the fact that the mollusc community changed through time at the core sites in response to shifting environmental conditions. Nevertheless, we encountered a number of taxa in the modern survey samples, which were absent from the sediment cores. This was probably a consequence of the limited spatial coverage of the cores and small diameter of the core barrels, which precluded sampling of large taxa. We report differences in mollusc abundance and taxonomic composition in the cores across space and time, which may be related to salinity changes in the lagoon and modifications of the nearby terrestrial environment.

The impact of chemical pollution on the European eel (Anguilla anguilla) from a Mediterranean hypersaline coastal lagoon

The European eel (Anguilla anguilla) is a critically endangered species. The impact of environmental contamination on this species has been highlighted as contributing to the decline in recruitment. The Mar Menor hypersaline coastal lagoon (SE Spain) is one of the most productive fisheries of European eel in Europe, making it a critical habitat for species conservation. The present study aimed to provide an initial overview of the impact of organic chemical contaminants on the European eel and the potential sublethal effects of chemical pollution on pre-migrating eels in this hypersaline habitat. We investigated muscle bioaccumulation of main persistent and hazardous organic contaminants (including some current-use pesticides) and genotoxicity, neurotoxicity, and xenobiotic detoxification system responses. The findings show that lagoon eels were exposed to high levels of legacy organochlorine contaminants, recently banned pesticides (chlorpyrifos), and some emerging chemicals. Some individuals surpassed the maximum levels of CBs authorized by the European Commission for human consumption. In this species, residuals of chlorpyrifos, pendimethalin, and chlorthal dimethyl have been reported for the first time. This field study provides relevant data to stock management and human health consumption and provides the first biomarker responses in European eel under permanent hypersaline conditions. Furthermore, the high frequency of micronuclei in peripheral erythrocytes of lagoon eels indicates sublethal genotoxic effects on the organism. Overall, the European eels growing and maturing in the Mar Menor lagoon are exposed to toxic and carcinogenic chemicals. The lack of seafood safety regulations for human consumption for some legacy chemicals that were measured in high concentrations in our study requires special action. Further biomonitoring and research are recommended to protect the animal, public, and environmental health.

Phytoplankton dynamics in the Mar Menor, a Mediterranean coastal lagoon strongly impacted by eutrophication

The Mar Menor hypersaline coastal lagoon has suffered serious degradation in the last three decades attributable to nutrient pollution. In 2015, the lagoon experienced an intensive bloom of cyanobacteria that triggered a drastic change of its ecosystem. Our analyses indicate that phytoplankton in 2016–2021 did not present a seasonal variability pattern; the community was mainly dominated by diatoms and punctually reached abundance peaks above 107 cell L−1 along with chlorophyll a concentrations exceeding 20 μg L−1. The predominant diatom genera during these blooms were different as well as the nutrient conditions under which they were produced. These high diatom abundances are unprecedented in the lagoon; in fact, our data indicate that the taxonomic composition, time variation patterns and cell abundance of phytoplankton in 2016–2021 differ notably in comparison to the data published before 2015. Consequently, our results support the finding that the trophic status of the lagoon has changed profoundly.

Molluscs Across Space and Through Time in a Hypersaline Coastal Lagoon, Mexico

Biotic remains have been used in paleoecological studies to provide information on past environmental conditions. Death assemblages can be used to make inferences about past environmental conditions if modern optima and ranges of taxa are known. Gaps in knowledge about historical biotic changes often stem from a paucity of information regarding species distributions, community species richness and evenness, community structure, ecological interactions, and possible factors that caused past biotic shifts. We studied mollusc assemblages in sediment cores from Río Lagartos coastal lagoon (Mexico) and compared them to present-day mollusc communities to gain insights into environmental changes that occurred in the lagoon throughout the last century. A total of 18,779 mollusc specimens, representing 20 bivalve and 45 gastropod species, and belonging to 32 families and 48 genera, were identified in three short sediment cores collected from the coastal lagoon in 2017. Molluscs in the sediment cores were compared to an inventory of modern fauna from the lagoon, which was collected along a salinity gradient in 2017 and 2018 to link species distributions with environmental variables. Mollusc communities from the sediment cores and present-day datasets possess the same ubiquitous species and feeding guilds. Nearly twice as many species, however, were identified in the sediment cores as in the present-day inventory. We report differences in mollusc abundance and taxonomic composition in the cores across space and time, which may be related to the salinity gradient in the lagoon, temporal shift in salinity, and recent human-mediated modifications of the nearby terrestrial environment. Biotic changes driven by shifts in salinity could have been reduced salinity. Such inputs may have been driven by hurricanes, along with associated high wind velocities and geomorphologic transformations. This paleobiology study will be of use for future conservation efforts in the coastal lagoon.

Woodchip bioreactors for saline leachates denitrification can mitigate agricultural impacts in mediterranean areas: The Campo de Cartagena-Mar Menor environmental issue

Leachates from intensive agriculture containing high nitrate have been identified as a major cause of the severe eutrophication crisis that impacts Mar Menor (SE Spain), the largest hypersaline coastal lagoon in the Mediterranean basin. A best management practice for removing NO3−-N is denitrifying bioreactors. This is the first study to assess the efficiency of citrus woodchips bioreactors in treating agricultural leachates that flow to the Mar Menor via surface discharges. Denitrification capacity, woodchip degradation (by weight loss), formation of potentially harmful compounds, and greenhouse gas (GHG) emissions were assessed. Three bioreactors (6 m × 0.98 m x 1.2 m) filled with citrus woodchips (3 m3 d−1 per bioreactor) through which the untreated ditch water over 1.5 years. Bioreactors were operated at 8 h, 16 h, and 24 h hydraulic residence time respectively, in each bioreactor. The main characteristics of the ditch water were: pH ≈ 7.5–8.0, electrical conductivity ≈ 5–8 dS m−1, dissolved organic carbon ≈6–10 mg L−1, and NO3−-N ≈ 22–45 mg L−1. Bioreactors were highly efficient in reducing NO3−-N. The average RNO3 in effluents was for the complete experimental period 8 g N m−3 d−1, 10.9 g N m−3 d−1, and 12.6 g N m−3 d−1 for 8, 16 and 24 h residence time, respectively. Nitrate reduction efficiency was modulated by seasonal changes in temperature, with an increasing efficiency in warmer periods (maximum ≈ 85–90% for all hydraulic residence time) and decreasing in colder ones (minimum ≈ 12%, 23% and 41% for hydraulic residence time 8, 16 and 24 h respectively). Woodchips degradation was greatest during the first six months (average ≈ 29% weight loss) in the material above the water level, attributable to aerobic mineralization of the organic carbon, while weight loss was ≈11% in woodchip media continuously below the water level. Dissolved organic carbon, sulfide, ammonium, and soluble phosphorus concentrations in the effluents were mostly low, although some peaks in concentrations occurred. Design consideration must be taken to avoid environmental impacts due to the occasional presence of harmful compounds in the effluents.

Molluscs along a salinity gradient in a hypersaline coastal lagoon, southern Gulf of Mexico

Abstract Molluscs are a diverse phylum in coastal lagoons because the numerous taxa collectively display broad ranges of optima and tolerance with respect to ambient conditions. We report on the taxonomic composition, habitat preferences and feeding guilds of molluscs from Río Lagartos coastal lagoon, Mexico. Molluscs were collected in the rainy season (September/October 2017), during the winter (Nortes) season (February 2018) and at the end of the warm, dry season (May 2018). Samples were taken using a Ponar dredge, a cylindrical PVC core barrel, or a beach seine. We studied the abiotic characteristics (sediment grain-size distributions, submersed aquatic vegetation abundance and salinity) to explore assemblage differences across the broad salinity gradient that characterizes the system (~30–78 PSU). Molluscs were represented by 39 species, 34 genera, 23 families and two classes. Stenohaline species were more numerous overall than euryhaline species, but their occurrence in samples was low (<20% of the samples). Stenohaline taxa lived primarily in environments characterized by marine salinity, and few were found under hypersaline conditions. We collected a smaller number of species than did studies carried out in the lagoon >35 years ago. Species accumulation curves revealed that the full species richness was not captured in our study. Euhaline environments displayed greater mollusc species richness and had a larger proportion of amount (mass) of submersed aquatic vegetation. In the hypersaline environments, species richness may be favoured by the lower dominance of sands. Suspension feeders were the most diverse group in both the euhaline and hyperhaline environments.

Use of the Sentinel-2 and Landsat-8 Satellites for Water Quality Monitoring: An Early Warning Tool in the Mar Menor Coastal Lagoon

During recent years, several eutrophication processes and subsequent environmental crises have occurred in Mar Menor, the largest hypersaline coastal lagoon in the Western Mediterranean Sea. In this study, the Landsat-8 and Sentinel-2 satellites are jointly used to examine the evolution of the main water quality descriptors during the latest ecological crisis in 2021, resulting in an important loss of benthic vegetation and unusual mortality events affecting different aquatic species. Several field campaigns were carried out in March, July, August, and November 2021 to measure water quality variables over 10 control points. The validation of satellite biogeochemical variables against on-site measurements indicates precise results of the water quality algorithms with median errors of 0.41 mg/m3 and 2.04 FNU for chlorophyll-a and turbidity, respectively. The satellite preprocessing scheme shows consistent performance for both satellites; therefore, using them in tandem can improve mapping strategies. The findings demonstrate the suitability of the methodology to capture the spatiotemporal distribution of turbidity and chlorophyll-a concentration at 10–30 m spatial resolution on a systematic basis and in a cost-effective way. The multitemporal products allow the identification of the main critical areas close to the mouth of the Albujon watercourse and the beginning of the eutrophication process with chlorophyll-a concentration above 3 mg/m3. These innovative tools can support decision makers in improving current monitoring strategies as early warning systems for timely assistance during these ecological disasters, thus preventing detrimental conditions in the lagoon.

Occurrence and Behaviour of Shorebirds Depend on Food Availability and Distance of Beaches from Urban Settlements

Coastal ecosystems provide important feeding opportunities for shorebirds, depending on their prey availability, hydrodynamic conditions and human pressure. We aimed to evaluate short-term responses (occurrence and minimum approach distance) of shorebirds to urbanization and natural drivers on an extensive beach arc adjacent to the largest hypersaline coastal lagoon of South America. The presence of the migrant Sanderling Calidris alba and resident Collared Plover Charadrius collaris was geo-coordinated and for each record and an equivalent number of random points we measured the distance from urban settlements, swash width and invertebrate abundance (food availability) in a snapshot sampling. The distance at which each shorebird flock escaped from humans was determined (minimum approach distance). The occurrence of shorebirds was predicted by food availability, and higher crustacean density was found in areas of shorebird occurrence (37 ± 19 individuals/m2) compared to random points (10 ± 10 individuals/m2). This result highlights the importance of the beach as a feeding area and the need for conservation of shorebirds' prey. The resident Collared Plover delayed their escape from humans in areas closer to urban areas, suggesting a higher tolerance to humans on disturbed beaches, where they can prioritize the food intake rather than vigilance. The larger flocks let the researcher get closer, corroborating the risk-dilution theory stating that flocking behaviour during foraging provides protection of birds from predators. In conclusion, our results showed that monitoring of sandy beaches based on shorebirds' presence and behaviour can be a reliable tool, especially close to coastal lagoons that constitute foraging sites for these charismatic species.

Eutrophication overcoming carbonate precipitation in a tropical hypersaline coastal lagoon acting as a CO2 sink (Araruama Lagoon, SE Brazil)

The carbonate chemistry was investigated in the semiarid eutrophic Araruama Lagoon (Brazil), one of the largest hypersaline coastal lagoons in the world. Spatial surveys during winter and summer periods were performed, in addition to a diurnal sampling in summer. The hypersaline waters have higher concentrations of total alkalinity (TA) and dissolved inorganic carbon (DIC) than the seawater that feed the lagoon, due to evaporation. However, TA and DIC concentrations were lower than those expected from evaporation. Calcium carbonate (CaCO3) precipitation partially explained these deficits. The negative correlation between the partial pressure of CO2 (pCO2) and chlorophyll a (Chl a) indicated that DIC was also consumed by primary producers. The uptake by photosynthesis contributes to 57–63% of DIC deviation from evaporation, the remaining credited to CaCO3 precipitation. Marked pCO2 undersaturation was prevalent at the innermost region with shallow, confined, and phytoplankton-dominated waters, with a strong enrichment of heavier carbon isotope (δ13C-DIC up to 5.55‰), and highest pH (locally counter-acting the process of ocean acidification). Oversaturation was restricted to an urbanized region, and during night-time. The lagoon behaved as a marked CO2 sink during winter (− 15.32 to − 10.15 mmolC m−2 day−1), a moderate sink during summer (− 5.50 to − 4.67 mmolC m−2 day−1), with a net community production (NCP) of 93.7 mmolC m−2 day−1 and prevalence of net autotrophic metabolism. A decoupling between CO2 and O2 exchange rate at the air–water interface was attributed to differences in gas solubility, and high buffering capacity. The carbonate chemistry reveals simultaneous and antagonistic actions of CaCO3 precipitation and autotrophic metabolism on CO2 fluxes, and could reflect future conditions in populated and semiarid coastal ecosystems worldwide.

"Greenhouse gas dynamics in a coastal lagoon during the recovery of the macrophyte meadow (Mar Menor, SE Spain)".

The Mar Menor is a hypersaline coastal lagoon with salinity values ranging from 41.9 to 45.5. The system is subjected to a high anthropic pressure that causes an intense eutrophication process, followed by a recovery of the macrophyte meadows. This study focuses on the distribution of the main greenhouse gases (CO2, CH4 and N2O) and was carried out in the extreme seasonal conditions of winter and summer during the year 2018. Sediment-water-atmosphere exchanges and biochemical processes in the water column appeared to be the main factors to explain the variability of these gases. Dissolved Inorganic Carbon (DIC), CH4 and N2O benthic fluxes values obtained in this study, were of 91 ± 29 mmol m-2 d-1, 3.9 ± 1.9 μmol m-2 d-1 and -0.65 μmol m-2 d-1, respectively, along with an important seasonal variation observed, with an increase of DIC and CH4 benthic fluxes during the summer season. Mean values of partial pressure of CO2 (pCO2) in surface water were of 579 μatm in winter and 464 μatm in summer, therefore we can establish that the Mar Menor acts as a source of this gas emitting 3.3 ± 3.0 mmol CO2 m-2 d-1 to the atmosphere. In spite of this, the Mar Menor has a strong autotrophic behaviour partly due to the recovery of the macrophyte meadows, presenting an estimated NEP of 101 mmol m-2 d-1. Regarding to CH4, the mean fluxes to the atmosphere were of 8.0 ± 5.8 μmol m-2 d-1 and there was evidence of CH4 production in the water column that increased in summer. Last of all, in the case of N2O the system acts as a sink with values of -0.65 ± 0.5 μmol m-2 d-1, presenting an intake of N2O that is usually detected in pristine systems.

Natural and anthropogenic effects on microplastic distribution in a hypersaline lagoon

Information on the transport and distribution of microplastics in coastal lagoons is scarce. This study provides the first evaluation of microplastic distribution in a hypersaline coastal lagoon and explores natural and anthropogenic factors that drive their location and transport. The study combines different field strategies: spatial distribution of microplastics in sediments, for September 2017 (wet season and peak use of the lagoon) and February 2018 (winter season, characterized by intense Northerly winds and least use of the lagoon); spatial distribution of microplastics in the water column in the winter season; ocean-lagoon exchanges of water and microplastics at the lagoon entrance during tidal cycles. Also, one-year records of water level variations along the lagoon provide connections between local pressure gradients and water fluxes. Statistical analyses indicate relationships between temporal variations of microplastic concentrations and human activities. Results show marked seasonality in sources and transport agents. During the summer, microplastics concentration was related to human activities. After this season, the accumulated precipitation in the continental karst region leads to an increase in the water level at the head of the lagoon. The resulting pressure gradient promotes seaward flushing of hypersaline water and of microplastics. At tidal (diurnal) time scales, measurements at the mouth of the lagoon revealed that more particles were collected in ebb than in flood. This variability underscores the need to resolve tidal variability for microplastic sampling in coastal lagoons and estuaries.

Role of small-sized phytoplankton in triggering an ecosystem disruptive algal bloom in a Mediterranean hypersaline coastal lagoon

Monthly samplings carried out in 2016–2019 and satellite color images from 2002 to 2019 have been combined to determine the onset and causative species of the ecosystem disruptive algal bloom (EDAB) that affects the Mar Menor coastal lagoon (Western Mediterranean Sea) since 2015. Substantial changes in satellite spectral reflectance attributable to increasing abundance of Synechococcus were registered in 2014. Furthermore, cell abundances of this species in 2016 were the largest ever obtained in the lagoon (6 106 cells mL−1), with values similar to those reported for other Mediterranean hypertrophic estuaries and coastal lagoons. These results suggest that the early changes leading to the EDAB started in 2014 and that Synechococcus played a relevant role in its development. Moreover, diatom and dinoflagellate abundances changed substantially in 2016–2019, ranging from 102 to more than 104 cells mL−1. Some of these changes were linked to flood, suggesting that EDAB has modified substantially the homeostatic capacity of the lagoon.

The onset of the Messinian Salinity Crisis in the central Mediterranean recorded by pre‐salt carbonate/evaporite deposition

AbstractThe Calcare di Base is a carbonate/evaporitic unit formed before the deposition of the massive halite bodies in the main depozones of the Mediterranean region, and has been at the centre of a fiery debate between different ‘schools of thought’ about its genesis, environmental conditions and timing of deposition. It crops out extensively in Southern Italy, across Neogene basins located on the Tyrrhenian and Ionian margins of northern Calabria, where it was studied through a detailed facies and stratigraphic analysis that revealed the presence of a continental/shallow‐marine to slope system, active during the onset of the Messinian Salinity Crisis. During the Calcare di Base deposition, an arid climate regime with intermittent humid phases occurred with a precession forced cyclicity, facing an overall generally cold climatic period. During arid periods, stressed environmental conditions permitted the establishment of widespread microbial‐mediated carbonate production, frequently associated with evaporitic (gypsum‐dominated) deposition, along a sabkha‐type environment with extensive salinas and hypersaline coastal lagoons grading seaward into a carbonate/evaporite shallow‐marine shelf. This is testified to by microbial boundstones and dissolution breccias commonly associated with nodular gypsum and arenites affected by desiccation, typically forming metre‐scale shallowing‐upward peritidal cycles. Seaward, gravity flow deposits are interpreted as re‐sedimented shelf limestones, defining a slope apron. Mixed carbonate/evaporite megabreccias and disorganized floatbreccias were deposited along the upper slope, whereas soft deformation with slides, slumps and channelized turbidites further developed along the lower slope to basin. During the humid climate episodes, that affected the platform system with a precession‐forced cyclicity, the carbonate production was reduced together with the evaporitic deposition, leading to the widespread deposition of marlstones and fine to coarse siliciclastic deposits.

The case of Mar Menor eutrophication: State of the art and description of tested Nature-Based Solutions

The Mar Menor (SE Spain), the largest hypersaline coastal lagoon of the Mediterranean basin, suffers a severe eutrophication crisis due to the nutrients that receives from the Campo de Cartagena watershed, mainly nitrate from intensive agriculture. This paper updates the state of the art in relation with nutrient discharges to the Mar Menor, and summarizes results from different tested Nature-Based Solution (NBS). Specifically, we show i) results from a pilot plant with woodchip bioreactors for nitrate-enriched brine denitrification, and ii) the first results obtained in a pilot plant with bioreactors and constructed wetlands for treatment of agricultural drainage water and leachates, as well as other effluents. Nutrient discharges to the lagoon are highly variable and occur via drainage network, drains, stormwater pipes, direct groundwater discharges from the Quaternary aquifer, and others. For instance, between January 2017 and January 2018 measured daily superficial discharge (floods excluded) ofN-NO3− amounted from 119 kg d−1 to 1084 kg d−1. Estimations subsurface discharges ranged 815 to 3836 kg N-NO3− d−1 in 2018–2020. Field studies in coastal wetlands (e.g. inflow ≈20–30 mg N-NO3− L−1, removal ≈80–90%) and results from pilot plants with bioreactors (e.g. inflow ≈30–40 mg N-NO3− L−1, removal ≈90–95%) and constructed wetlands (e.g. inflow ≈30–40 mg N-NO3− L−1, removal ≈60–70%), showed the good performance of these systems for nutrient retention. Four strategies are considered for reducing nutrient inputs into the Mar Menor, which include a combination of nature-based solutions and best management practices. (i) Reducing the leaching of nitrate to the aquifer and export of nutrients and sediments following heavy rains by improving fertilization, and irrigation routines, and soil conservation measures in the agricultural fields. (ii) Development of effective and scalable tools for denitrification of nitrate-rich brine produced by on-farm desalination plants. (iii) Capture and treatment of polluted water discharged to the Mar Menor via hydrologic networks, subsurface flow, drainage ditches, and others. (iv) Preservation and restoration of coastal wetlands.

Variability of the thermohaline structure of a coastal hypersaline lagoon and the implications for salinity gradient energy harvesting

Natural and artificial systems containing water resources that have different salinities can be used to generate salinity-gradient energy (SGE). In this paper, the feasibility of implementing SGE in hypersaline coastal lagoons is addressed, taking the coastal lagoon La Carbonera in Yucatan, Mexico, as an exemplary case. A realistic approach to the exploitation conditions and potential that could occur in a SGE plant in these ecosystems is presented. We first analyzed the variability of salinity and temperature in the three characteristic zones of the coastal lagoon and the correlation of these variables with atmospheric forcing. This was done using 1 year records of in situ measurements. Then the theoretical potential for SGE and the intra-annual variability of that potential were assessed considering the three possible harvesting configurations of mixing among fresh, sea, and hypersaline water. Results show that the thermohaline structure may vary significantly for the three locations at different time scales (diurnal to seasonal) depending on the tides, winds, air temperature, atmospheric pressure, and solar radiation. That suggests that the highest annual energy yield would be obtained from alternating throughout the year among the mixing configurations, depending on the specific seasonal thermohaline structure of the lagoon.